It is generally known and acknowledged that patients involved in respiratory therapy require the inhalation of life-supporting gases, generally including oxygen and/or air. It is further known that it is far more beneficial for the patient to receive such gases under conditions of heat and humidity rather than to supply the patient with merely a dry cool gas. It has been found, for example, that when the inhaled gas is both heated and humidified, the patient is more receptive to the gas especially in connection with minimizing other potential respiratory diseases when involved in respiratory therapy. The present invention is a device which seeks to improve upon known systems for providing both heated and humidified gases to a patient involved in respiratory therapy, or involved in other systems wherein there is a requirement for the provision of life-support gases to be inhaled.
To date, no device has been developed which permits the operator thereof to readily adjust the system to provide inhaled gas at a given temperature and relative humidity. Devices of this type to accomplish humidification have generally been nothing more than humidification boxes through which a gas is bubbled via a gas inlet directing the gas into the humidification chamber, bubbling the same through heated water and the heated humidified gas being captured in a gas outlet and directed to the patient. It will be appreciated that in order to vary the temperature and/or humidity level of the gases, a great deal of manipulation is necessary as well as time, since it is not possible to, readily, change the temperature of the exiting gas without first changing the temperature of the water through which the gas is bubbled. For example, such devices generally require that the operator change the temperature of the heater in order to further heat the water in the chamber which accomplishes both higher heat level for the gas as well as a higher humidification level. It will, therefore, be appreciated that it has not been possible to independently control both temperature and humidity with such devices.
Another problem associated with such systems is that once the heated and humidified gas exits the humidifier and travels the path to the patient's support system such as a face mask or the like, the gas has a tendency to cool which causes a condensation of water in the patient's gas delivery tube.
Exemplary of the types of devices presently employed in solving the problem of heating and humidifying the gases to be inhaled is shown in U.S. Pat. No. 3,659,604. It will be observed that the device disclosed and claimed therein involves the provision of a heating chamber wherein water is contained, the water being heated by a heater and gas being introduced into the chamber, picking up moisture from the humidification element, and exiting the system through a gas outlet for passage on to the patient. In order to prevent the gas from losing temperature as it traverses the hose connected to the patient, a heating element is provided in longitudinal arrangement in the exit hose such that gases are heated for a distance as they pass to the patient. It will be appreciated that even with this system, efficient and rapid variation of the temperature and/or humidity is difficult, if not impossible since it still involves the requirement of changing the temperature of the water within the chamber in order to affect the commitant change in the temperature of the gas. Furthermore, the subject device does not actually control the relative humidity of the gas, but only the humidification level of the gas which passes through the system.
Other types of systems available basically fall into two categories, these including the cascade type system which is used mostly on ventilators and the bubble type system which is generally used with a compressed oxygen/air system. Both of these systems operate only when gas under pressure is delivered to the system either from a ventilator or from an oxygen/air source where the gas is under a pressure of at least 50 psi. Heated nebulizers have the advantage of clinically allowing oxygen/air gas mixing from a single compressed oxygen source, however, these units can and do introduce contamination from the water reservoir to the patient via the water particles generated. In generally all of these systems, the temperature of the gas is controlled by controlling the temperature of the water reservoir with an adjustable thermostat. As indicated previously, this method is slow in reaction time and also creates a possible safety hazard by exposing an adjustable thermostat to a wet, oxygen-enriched environment.
The proposed system of the present invention combines the advantage of existing systems but includes unique and new design and functional concepts. In short, the unit of the present invention allows the operator to have an effective fast safe control over several parameters of the system and the gases which flow therethrough. The present system offers a strict water vapor generation with controlled oxygen/air mixing from a single compressed oxygen source. In addition, the temperature control eliminates any exposed adjustable thermostat, but does allow the operator to adjust to any delivered gas temperature from 85.degree. to 114.degree. F. in less than ninety seconds. In addition, the heat control system of the present invention operates at low heating element temperatures thereby allowing the heater to operate safely with no gas flow through the humidifier. Hence, preheating of the humidifier is possible without any danger or other hazards existing. Finally, as to the heating element, it will be noted from the description following below that the heating element is located externally to the sterile humidifier such that the heater need not be sterilized for subsequent use.
The present system also allows the operator to control the relative humidity of the delivered gas. By using the fast reacting temperature and relative humidity controls, the delivery gas can be regulated to meet most clinical situations. For example delivery gas could be regulated to 108.degree. F. at 80% relative humidity when this gas flows through the delivery tubing it would be cooled. As the gas cools, the relative humidity would increase and the gas at the patient end of the delivery tubing would be at 98.degree. F. and 99+% relative humidity. A further advantage is the fact that no condensation occurs in the delivery tube.